Induction furnace construction



April 17, l945 H. A. sTRlcKLAND, JR

INDUCTION FURNACE CONSTRUCTION l12 Sheets-Sheet l Filed March 18, 1943 I INVENTOR Harod Srwfland J'.

A TTORNE Y April 17, 1945.

H. A. sTRlcKLAND, JR 2,373,719

INDUCTION FURNACE CONSTRUCTION Filed March 18,1943 2 sheetssheet 2 A TTORNE Y Patented pr. l?, i945 'l UNITED STATES PATENT ori-ica 37ans INDUCTION FURNACE CNSTRUCTION Harold A. Strickland, Jr., Detroit, Mich., assigner to Budd Wheel Comp any, Philadelphia, Pa., a.

corporation of Pennsylvania Application March 18, 1943, Serial No. 479,556

(Cl. 21B- 13) 14 Claims.

This invention relates to electric induction furnaces and particularly'to furnaces of this type adapted for heating billets, -bars yand similar stock to forging temperatures.

In furnaces utilizing inductive heating means the inducing coil is usually arranged and supported so as to receive the billet or other charge or workpiece within the chamber formed by the convolutions of the coil. It is accordingly necessary vthat this coil be self-sustaining, that it be properly cooled to prevent overheating, that adev quate head insulation be provided for protecting the supporting structure, and that the whole arrangement of coil, insulation, cooling devices and support be strong, rigid'and free ofv cumbersome or bulky elements.

Accordingly, the objects of the invention may v be enumerated as follows: to provide a self-sustaining induction furnace structure which permits elimination of internal supporting elements:

to provide a structure which is stressed radially in order to effect rigidity in the component structural elements; to provide improved furnace end supports permitting elimination of bulky external elements; t provide end support means which serve to protect coil turns and external supporting elements from flame corrosion; to permit insertion and removal of firebrick from a furnace end with limited disturbance' of theA support means; and in general "to provide a rigid, compact,` self=-sustaining furnace chamber construction with a reduced number of essential parts.-

The above objects are realized in an arrangement, which may be preferred, hereinafter described and 4illustrated inthe accompanying drawings in which:

Figure 1 is a horizontal section through the heating coil and associated supporting structure; Figure 2 is an endA view of the heating coil showing the front cooling rail terminals;V

Figure 3 is a section on lines 3-'3 of Figure 1 illustrating the coil supporting rails and insu'- lating structure;

Figure 4 is a detail of the rear rail attachment means; and

Figure 5 is a. view of a rail prior to assembly in the heating coil unit. In my copending application Serial No. 384,503,

and Patent No. 2,365,Q21 issuedDecember 12,

1944, a division of said application, there is disclosed an arrangement of furnace parts which in many respects is satisfactory and which forms the basis of the improved arrangement as disclosed herein. As shown in said copending ap' plication and patent and in the drawings accom- -panying this application, the heating unit I0 is .I

substantially tubular in form having a front open end and a closed rear end, the workpiece being adapted for insertion through the open end into the. interior of the heating chamber. In the form of the invention as shown in Figure 1 the heating unit includes a continuous coil of tubing .H the same being of square section although suitable insulation material, as "micarta or other mica containing or phenolic layered sub- .stance the outer layer being held in position by means of rtape i3 -as moreclearly shown in Figure 3.

Interiorly of the coil IIl is a layer i4 of mica, or mica containing composition which is resistant to heat as well as electrically insulating. Within the layer it is an additional layer of mica or mica containing composition l 5 which is prei'- erably-even more resistant to heat than layer 5.

Alternatively both layers It and l5 may be made of glass lbre or a similar product. .y

The coil supporting structure is contaifned within the insulation layer l5 and consists of a plurality of axially extending rails. I 6' which as shown are of tubular construction with a. circular cross section. Referring to Figure 5 it will be seen that these rails have a slight curvature from end to end the center of the curvature being on the inner side of the rail as positioned in Figure 1.

On this inner sidealso are attached a series of supporting elements il and I8, the support Il' being intended for the retention of a fire brick as will be explained more fully hereinafter and the element t8 serving as a support and guide for' the workpiece. It is noted that the forward `or front end of the support I8 has an inclination .I9 which serves to facilitate entry of the workpiece into the heating chamber. The support I8 as more clearly shown in Figures 2 and 3 is inthe shape of a flat plate the'edge of which opposite the inclined edge is being welded er otherf Wise attached to the inner surface of the rail i6.' The rear end ,2U of the rail is straight in extension of the main body of the rail structure whereas the front end 2l' of the rail is outwardly turned to aord a radial connection to -tubing containing cooling fluid. Also at the angle of out turn of the front rail end at 2l. there is positioned a lnger'22 threaded at its outer end which is adapted for connection to the end supports as will now be described.

The assembled structure of coil insulation layers and rails is supported by en d plates t and Si, the end plate 3b covering the front end of the coil and the plate Si the rear end. These plates are similar in construction being substantially square in outer outline as shown in Figures 2 and 3 with relatively large central openings coinciding with the heating chamber of the coil interior. These end plates are made of electrically-non-conducting material which is also heat resistant and which moreover is structurally adequate for the support of the assembled coil structure. These plates are retained in position on the endsrof'the heating coil 'by means of external rods three of which are indicated in Figure 2 bearing the numeral 32, thisV figure showing the heads of the rods and Figure 1 showing the screw threaded rear ends 33 of 'the rods.` Coil springs 3d are interposed between the rear end plate 3l and the retaining nuts 35 on the ends of the rods so that accommodation may be made in the structure for expansion due to heat.

t Radial support for the coil construction is provided as hereinabove mentioned in the rails lo which extend axially within the innerinsulation layers and in contact therewith \wit h their ends'- protruding forwardly and rearwardly sertion in the furnace the same having. axially curved inner and outer surfaces 52 and 53 lthe inner'surface 52 having its edges inwardly recessed and outwardlyinclined to formseats for the wings 5@ of the retaining clips il, It will be seen that this type of brick construction permits insertion of the brick by sliding the same from the ends of thefurnace coil so that in the final formation of the; inner surface there is a construction having alternate segments of continuous iire brick and metal rails cooled by the pasl sage of a cooling iiuid. This construction while including diierent materials such as metal and ceramic substance nevertheless combine, to form a heat resistant surface of considerable eiectiveness.

The heating coil as a whole may be supported by various means. vFigure l suggests one. method of support by use ofsupporting arms 5d which underlie the heating coll unit. Attached to the supports 56 are risers 55 to whichare secured the bus bar assembly 56. As shown in Figure l this assembly includes -busvbars ol and 53 spaced by insulation 59 the assembly being attached to the risers 55 by bolts o@ passing through the insulation tube 6l and spacedfrom the bus bars by insulation washers 62. Connection to the bus bars 57 and 58 from the ends of the heating coil ll is made at the terminals thereof. As shown 0 in Figure 1 therear end 'l0 of the coil is clamped throughthe central'openings in the end plates 3@ and 3l, The f ront end of the rail is fastened to the front end plate t@ by means kof ybolts it which are positioned adjacent the outer edge of the end plate and which bolt clamps t? through which y the finger 22 of the rail extends and to whichrthe finger is fastened by the nut Sti. The rear end of the rail projecting from the end plaie 3i is secured to the end plate by means of a hook t@ which underlies the rail end and projects under the clamps et to which it l`is secured'by the nut di. It is pointed out that the showing of Figure directly by clamp 'il to aiitting i2 bolted to the |bus bar 58, the coil extending into the coupling I3 at which connection is made to the cooling. fluid conduit at ld. Likewise the front end lli 5 of the coil is clamped to the' fitting i@ andleads into the coupling i'i and the inlet cooling uid conduit i8, The powerintake is from the tubular l concentric risers s hown'in dotted. outline in Figure l the same extending in dual plates 3l and d2, plates 8l being bolted to bus bar 5l and plates 92 to bus bar 58.

There is shown additionally in the construction at the rear end of thefurnace chamber an 45 ejector rod 96 slidably movable in a combination l of the -rail in assembled position is different from the showing oi the rail in Figure 5, this being due to the fact' that in assembly the tension of the hook 39 and finger .22 when the nuts are drawn taut causes a straightening of the curva' ture of the rail with the result that the center sec- -tion of the rail is strongly compressed on its outer stock gauge and support 9i the purpose oi the* ejector being to force `out the workpiece from the heating chamber upon completion of the desired heating cycle. it the frontend of the furnace there is also shown a portion of the front Iplate @2 and the mouth piece plate 93 with the rearwardly and inwardly projecting guide fingers @t connected to center the workpiece in its movement surface against-theload of insulation and coil thus insuring a tight, compact and solid assembly M oiz the coil unit. s

As described upto this point the internal sur-- face of the heating chamber is formed oi the' rails and the enclosing Ymica insulation casing. To complete the :interiorv surfacing of the heating chamber ilre brick d is inserted preferably at the ends of the furnace vchamber so as tolie'- between Vthe adjacent rails 'and to lll the space vbetween the mica casing it and the concentrical surface defined by points concentric but inwardly displaced from the circle including the Ainner edges of the rail guides l@ 'as shown in dotted outlinein Figure 3. To this en'd the clips il hereinabove mentioned are shaped in at in-v wardly extending 4strips forming wings E@ (see Fig. 8) which are rigid with theV rails it and form therewith inner supports for the nre brick edges.-

'I'he nre brick 62 is formed particularlyv for in into the chamber interior. It is noted that the mouthpiece plate at the point of contact with the front wall 92 has aninwardly offsetcircumferenf tial recess permitting some degree of radial ad# justifient ofthe mouthpiece for centering purposes.. 1

It is noted also that the locus of rail support inner edges it i'orms a cylinder the axis of which is offset upwardly from the'heating coil axis in order to insure axially symmetric positioning of the workpiece as indicated indotted outline 95 rin Figure 3. J l A Attention is directed 'to the continuity of the fire brick and rail supporting structure both axially and circlmiferentially. Actual usage has demonstrated the, importance of maintaining on if@ the linner surface of a furnace adjoining the.

i5 theiire'bricks atthe break tendedto fuse and may be made l sion.

. assays@ disintegrate, thus causing more or less frequent shutting down of the iurnace to make necessary lining repairs.y This factor is of additional im portance because of the length of the furnace, auxiliary supports, causing a break in the continuity of the break structure, being placed at the approximate center 'of the axial length of the lining. Avoidance is made of construction necessitating a central break in the lining by usage of the rails having a normal outward convexity so that in the process of assembly the whole central area of the brick lining structure andI associate'd casings and coil are placed under radial pressure thus overcoming any necessity for additional central supports. This results also in greater compactness of the unit in the iinal assembly. It is pointed out further that in case the re brick is relatively loose in the guideways the rails would tend to assume their normal outward curvature giving a slightly bowed or arched enect axially of the furnace which would also tend to maintain the central sections of the coil structure.

The described arrangement has been found to be useful, operative and effective but it is apparent that modifications as to detail may and therefore limitation is not intended in the disclosed embodiment except insofar as imposed by the claims hereunto appended.

What is claimed is: A l. An induction furnace comprising a tubular 'heating coil, heat resistant rails axially positioned interiorly of said coil and forming a grill therein, heat insulatingfmaterial between and supported by said rails, and end plates attached to said rails for supporting said rails and material.

2. An induction furnace comprising a tubular heating coil, metal rails axially positioned interiorly of said coil and forming a grill therein, heat insulating material between and. supported by said rails, and end plates attached to said rails for supporting said rails and material, saidy rails extending outwardly at the ends through apertures formed in the end plates, the rail ends, insulating material and end plates at the mouth end of the furnace chamber forming a shield for the prevention of corrosion at the adjacent furnace end.

3. An induction furnace comprising a, tubularl heating coil, heat resistant rails each having an unstressed radially outwardly convex bend from end to end, positioned axially within` said coil and insulated therefrom, heat insulating material interposed on the coil wall between said rails, said materialv being supported by said rails, apertured plates at each end of said heating coil, said rails extending through said plate apertures, and means for. attaching the rail ends to said plates under radial tension. Y

4. An induction furnace comprising, an electrical tubular heating coil, heat resistant rails axially positioned interiorly of said 'coil and forming a grill therein, heat insulating material between and supported by said rails, end plates at- ;,tached to said rails for supporting said rails and material, andmeans for holding said end plates in yielding co'relationshipv whereby adjustment rfor axial rail and coil heat expan- 5. In an induction heating furnace a tubular heating coil, metal rails laterally spaced' in axial relationship within and adjacent said coil, electrical insulation between rails and coil, low heat conductive and heat resistant material between said rails, means secured to the rails-for holdingv be made said material `between the rails, said rails having an unstressed radially outward convexity,- means for supporting said rails under strain to reduce said rail convexity, and workpiece supports secured to said rails in spaced relationship along said rails whereby said' rails are free to ilex radially of the coil;

6. In an induction furnace, an electrical tubular heating coil, supporting metal rails forming a grill positioned axially within and adjacent to, but electrically insulated from said coil whereby electrical contact between coil and rail is prevented, heat resisting and insulating material supported by said rails and forming continuous axial layers therebetween, whereby a complete furnace chamber lining of said rails and material A the rail adjacent t brick supported by is formed, and means at the ends only or said heating coil for holding said lining in position adjacent said coil.

7. In an induction heating furnace, a supporting heat resistant rail for fire brick and the like comprising an extended member having a small degree of curvature from end to end, an end curved sharply in the direction or maximum rail curve convexity, and a support element fixed to the point of end curvature and coplanar with said curved end and rail.

8. In an induction heating furnace, an electrical tubular heating coil, axially extending and laterally displaced metal rails positioned within and adjacentto but insulated from said coil and forming a grill framework therein, heat resisting and insulating material between, and supported by said rails whereby the coil is insulated from said rails, an integral finger' attached to one end of the rail, heat and electricity insulating coil end plates having apertures for receiving the rail ends, said rail ends extending through said pla apertures, and radially adjustable support means at either end plate for attachment to the linger at one end and to the rail at the other end for supporting the adjacent rail end and imparting radial movement thereto.

9. In induction iurnaces, an electrical tubular heating coil, a, continuous heat resisting and heat insulating layer within and adjacent said coil and electrically insulated therefrom, and means at the ends only of said coil for holding said layer in position adjacent said coil.

10. In induction furnaces, an electrical tubular heating coil, a continuous heat resisting and heat insulating layer within and adjacent said coil and electrically insulated therefrom, and means at the ends only of said coil for holding said layer in position adjacent said coil, said layer including 'electrically conductive and nonconductive elements. l

11. In induction furnaces,l a tubular heating coil, axially extending and laterally displaced heat resistant rails positioned within and adjacent to but electrically insulated from said, coil, fire said rails therebetween and between the rails rails are spaced by an axial segmentvof' single bricks, and means including insulation end plates for supportingsaid rails at the coil ends only whereby said` bricks may be placed in position inside the coil from the coil end.

l2. In an induction furnace, a tubular heating coil, a, plurality of axially extending rails forming a grill adjacent the interior surface of said coil, insulation material supported between the coil and grill by said said grill in place.

13. In an induction furnace, a tubular heating and coil, whereby adjacent grill and means at the coila y coil, a plurality of axially extending rails forming a grill adjacent the interior surface of' said coil, insulation-material supported between the coil and grill by said grill and support means at v the coil ends for holding the insulation material in close proximity to said coil,rsaid rail@ being normally curved outward convexly with reference to the coil axis whereby the rail ends are under pronounced radial inward tenion when supported in position by said rail support means.

14. Aninduction furnace comprising a tubular heating coil, heat resisting rails axially positionedinteriorly of said coil and forming a grill therein, heat insulating material between and supported by said rails and extending to the coil ends, and end plates attached to said rails for the support thereof, said coil end plates overlapping the coil ends and extending to the insulating material whereby a, tubular protective shield is formed at the coil ends.

HAROLD A. STRICKLAND, JR. 

